Hall Sensors are the industry choice for medium sensitivity magnetic sensors due to low cost, small area, and easy integrability. However, all semiconductor Hall sensors suffer from offset resulting from nonidealities such as mismatch, doping variations, and undesired piezoelectric effects. A technique referred to as “spinning current” partially reduces the offset at the expense of severe bandwidth degradation. Even the residual offset is large enough to limit accuracy in most of the application. Moreover, the residual offset drifts depending on factors such as temperature, packaging, stress, variation, and aging.
The so called “Hall Effect” occurs when a magnetic field is oriented perpendicular to an electric current. The magnetic field generates a voltage difference across a conductor, called the Hall Voltage, in a direction which is perpendicular to both the direction of the magnetic field and the direction of the current flow. By measuring the Hall Voltage it is possible to determine the size of the component of the magnetic field. Typical Hall sensors usually include a strip or plate of an electrically conductive material with an electric current flowing through the plate. When the plate is positioned in a magnetic field such that a component of the field is perpendicular to the plate, a Hall Voltage is generated within the plate in a direction that is perpendicular to both the direction of the magnetic field and the direction of the current flow.
Semiconductor Hall Effect sensors produced using current techniques typically include a sensing element produced from silicon. The magnetic sensitivity of these devices is directly related to, and limited by, the electron mobility, mu, of the material used to construct the sensing element. Silicon typically has an electron mobility of approximately 1500 cm2/(Vs). Graphene, by contrast, may have an electron mobility in the range of 4500-40,000 cm2/(Vs). Consequently, a Hall Effect device employing a sensing element constructed from graphene will have a much higher magnetic sensitivity than a typical silicon based device.
Hall sensors using graphene as the channel are expected to provide good noise performance, depending on the achieved mobility. However, Graphene Hall sensors also suffer from the same offset problem of semiconductor Hall devices.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.